1. Field of the Invention
The invention relates to oil field communication with downhole tools. More particularly, the invention relates to a communication/actuation system wherein vibration is the transmission media. Vibrations provide instructions downhole in a reliable manner for communicating such instructions to downhole tools which then activate. The invention is also directed to more general surface-to-downhole and downhole-to-downhole communications.
2. Prior Art
The prior art teaches one of ordinary skill in the art to provide an apparatus at the surface or other location in a wellbore, to generate an acoustic pressure pulse coupled to the fluid (i.e. liquid) in the tubing string. The pulse is carried downhole to a tool having strain sensors therein capable of sensing the pulse or pulses as they reach the sensor. A programmed sequence of pulses will be awaited by the tool prior to actuation. Upon sensing the programmed sequence, the electronics package in the tool signals an actuation of the tool. This system is set forth in more detail in U.S. Pat. Nos. 5,579,283, 5,343,963 and 5,226,494, all of the contents of which are fully incorporated herein by reference.
While the systems(s) disclosed in the referenced patents are very effective in many situations, they fail to be reliable when there is a gas bubble in the fluid column. As one of ordinary skill in the art will appreciate, the acoustic pulse travels well in its host (liquid) medium but suffers significant losses when crossing an interface with another medium as is the case when there is a xe2x80x9cbubblexe2x80x9d of gas (e.g. Nitrogen) in the tubing string. When this condition is present, little if any of the message from the surface is effectively communicated downhole because the pulse has been so attenuated by the gas bubble(s) that it lacks sufficient magnitude to be sensed by the strain gauges on the downhole tool. This is, of course, if indeed any portion of the pulse reaches the strain gauges at all. This has been problematic in some wells and therefore needs a remedy. What is needed is a communication means for operating downhole tools that is unmitigated by the type of fluid or hardware through or around which it propagates.
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the remote actuation/communication system of the invention. The invention provides reliable communication to downhole tools by employing vibration initiators and vibration receivers. The vibrations are created generally at the surface by either an acoustic pulse machine like that disclosed in the prior art listed above or by operating a pump or other machinery. The vibrations are coupled to the well annulus by a hose connected to the vibration generating device and to the well fluid. The hose generally is filled with water but could be filled with another liquid as desired. The liquid in the hose conveys the vibration from the vibration generating machine and transmits the vibration to the well fluid. The vibrations are then propagated downhole naturally in the liquid of the wellbore or in the tubing string. Where an acoustic pulse is employed, it travels down fluid in the annulus of the well in much the same way it travels in the tubing fluid in the prior art. An astute reader will recognize two apparent problems: one is that there may be gas in the annulus which presumptively would create the problem associated with the prior art and two that there may be packers or other hardware located in the annulus that would defeat propagation of the pulse. If strain gauges were used in the invention and waited for a pressure pulse, the concerns set forth would nearly certainly be wrought out but because the invention employs accelerometers to sense vibrations as opposed to pressure pulses, the message is receivable by the downhole tool intended to receive the signal. More specifically, although the pressure pulse would be lost (in a gas bubble) or reflected (e.g. by a packer) the vibration associated with the pulse is coupled to the pipe itself and is propagated through any pulse attenuating areas that would stop or reflect a pressure pulse because the tubing string is continuous. By employing high frequency or high band width accelerometer(s) in vibratory communication with the propagation medium and in electrical communication with a downhole microcontroller-based vibration receiving system, it is possible to reliably provide information to the downhole tool. The microcontroller in a downhole tool will be programmed to await a certain series of signals from the accelerometer and then actuate the tool. By creating pulses with a vibration source, the vibrations associated therewith are sent downhole and sensed by the accelerometer. Similarly, if the vibrations are caused by other machinery they are still received by the accelerometer, which provides a signal to the microcontroller for each vibration event sensed. Alternatively, and more economically, due to the avoidance of the need for the pulse apparatus or other specialized equipment, the rig pump, which, as is appreciated, is already on the rig, may be employed to create the vibrations.
Vibration is inherent in the pipe when fluid is circulated by the rig pump. Therefore, if the pump is turned on and off a number of times and for certain amounts of time to match a programmed vibration sequence in the downhole tool, the accelerometers will pick up the vibration and the tool will actuate. This is a particularly important alternative for smaller drilling companies due to the expense of renting and transporting the pulse apparatus and paying for the technician to run the rented equipment.